I didn't add it to the documentation because I don't want to encourage its use. The specialized form of the macro should not be necessary once DST is implemented, because the `write` macro should look like:

```rust
macro_rules! write( ($dst:expr, $($arg:tt)*) => ({
    let dst = &mut *$dst;
    format_args!(|args| dst.write_args(args), $($arg)*)
}) )
```

You'll not the initial dereference plus `&mut`. This will cover all use cases of the `write` macro, as used today, while only borrowing the specific field of a struct. The downside is that you can use a trait object with `write!` today, but you cannot dereference it.